An absorption refrigerating system utilizing hot water obtained by a solar heat collecting apparatus or warm water such as warm waste water as a heat source, has generally been widely applied, owing to low cost of such driving heat source.
However, as to such heat source of warm water, there is a disadvantageous case where the temperature of such warm water is too low or a sufficient heat value cannot always be obtained when required. Therefore, in order to operate such absorption refrigerating system dependent on the amount of load, a high temperature heat source utilizing steam, combustion gas or fossil fuel has generally been used in combination with a low temperature level heat source. When operating such absorption refrigerating system by using fossil fuel, it has been desired to perform a double-effect operation to enhance the operational efficiency.
On the other hand, when the absorption refrigerating system is operated only with a heat source of low temperature warm water, the temperature of such heat source is too low and subsequently it is difficult to perform a double-effect operation.
Therefore, it has generally been practised to select the operational mode of an absorption refrigerating system by a specially disposed selector valve such that a single-effect operation is performed when low temperature warm water is used as a driving heat source, and a double-effect operation is performed when a high temperature heat source using fossil fuel is used as a driving heat source. However, such provision of the selector valve is not preferable, because not only the switching operation of the selector valve is troublesome, but also the absorption refrigerating system becomes complicated in construction.